There exists in the coal industry an increasing need for a process to clean and wash fine coal. This fine coal can be defined as particulate coal ranging in size from 0 to 14 inch and may be further classified into two categories: namely classified fine coal (28 mesh to 14 inch), and classified ultrafine coal (0 to 28 mesh). Coal particles within the fine range are being produced in larger and larger quantities due to the increased use of continuous mining operations. In addition, current economic trends in the energy market make it more feasible to reprocess the waste piles from previous coal processing operations to recover the fine coal particles that have been discarded and until the present invention have not been economically recoverable.
Raw coal may be processed by a number of methods which may include: crushing, jig washing, dense media washing, sifting, flotation, centrifuging, magnetic separation and drying. The first of these processes crushing, leaves the coal in an assortment of particles and lumps which may range from microscopic to several inches in size. At this point in the process the raw coal still contains a large percentage of undesirable matter commonly referred to as ash. This ash must be separated from the coal as efficiently as possible to obtain a pure coal product suitable for combustion. The aforementioned washing, sifting, flotation, centrifuging, and drying are techniques used to separate the coal from the ash and to prepare the coal for combustion. These separation techniques can be divided into two categories, wet processes and dry processes.
Dry processes generally include dry cyclones, sifting, and shaker tables such as the vibratory screen as disclosed in U.S. Pat. No. 3,113,098 issued Dec. 3, 1963 to Ffoulkes. U.S. Pat. No. 3,901,794 issued Aug. 26, 1975 to Hemme et al. discloses an example of a circulatory air sifter of the type that may be employed in dry coal processing or similar operations.
Wet processes generally include jig washing, dense media flotation and cyclones. Most wet processes also include various recovery and filtering systems in order to efficiently recycle the fluid used in the process.
The large majority of current coal processing plants use a wet process to clean the coal. Ultra-fine particles that enter into the wet processes cause inherent problems in subsequent handling of the fluids used in these wet processes. The fluid circuits in such processes become unwieldy and costly. One such example can be found in U.S. Pat. No. 4,217,207 dated Aug. 12, 1980 and issued to Liller. Thus, there does not exist in the art, an efficient method to eliminate the ultra fine particles in a wet process.
Past coal processing plants have discarded a large amount of fine coal particles along with the separated ash and debris. Current economic trends in the energy market dictate that a feasible process is needed to reprocess fine coal from waste piles of previous coal operations in order to recover the fine coal which is present therein.